Generally, mechanical and/or chemical treatments of cellulosic plant substances (e.g. wood) are used in the papermaking process to generate pulp, the basis and raw material for making paper products. Pulp may be generated either chemically or mechanically by removing the cellulose fibers from the wood matrix, which typically occurs in a refiner. In the context of the paper and pulp industry, a “refiner” is a piece of equipment used to grind up wood, typically wood chips, between two rotating surfaces (e.g., rotating discs) having refiner plates attached thereto. In particular, a disc refiner uses two refiner plates for treating pulp and paper fibers in order to develop strength in the paper product made from such fibers. The fibers pass between two plates, one or both of which rotate and apply pressure to the fibers. Thus, the liberation of fibers from a wood matrix is commonly referred to as “refining”.
The chemical treatment of wood, also referred to as chemical pulping, essentially uses chemicals in the digestion of wood where solutions of various chemicals eliminate or dissolve lignin, non-fibrous materials or other impurities to result in the generation of pulp. Mechanical treatment, also referred to as mechanical pulping, utilizes a grinding mechanism such as the above-described disc refiner to liberate fibers from a wood matrix, wherein the pulp is liberated via mechanical force rather than by chemical means.
Typical mechanical processing systems consist of several steps, including wood chipping and handling, mechanically sorting the wood chips, washing the chips, preheating or steaming (atmospheric or pressurized) of the chips, 1st stage refining, an optional 2nd stage refining (often multiple refining stages are used), latency removal, screening, bleaching, and storage before the pulp is sent to a paper machine.
As known in the art, mechanical pulping processes require the consumption of a significant amount of energy. There is a desire within the industry to reduce these energy requirements to generate the pulp necessary for the production of paper and paper additives. Attempts have been made in the art to reduce the energy demands of refiners, as described in U.S. Pat. No. 4,388,148 (Yahrmarkt et al.); U.S. Pat. No. 5,007,985 (Engstrand et al.); U.S. Pat. No. 5,338,405 (Paft et al.); U.S. Pat. No. 5,454,907 (Hayashi) and U.S. Pat. No. 6,159,335 (Owens et al.).
Another method of realizing energy savings is to increase the production rate of a refiner without increasing the specific energy consumption, as specified in the technical article titled “The Effect of Production Rate on Specific Energy Consumption in High Consistency Chip Refining”, by Strand B. C. et al. IMPC Conference, Oslo 1993, p. 143-151. Thus, the refiner would provide a greater amount of pulp without a simultaneous increase in the specific energy consumption. There have been attempts within the industry to increase the production rate of a refiner, as is described in U.S. Pat. No. 3,808,090 (Logan et al.), however, such attempts have proven unsuccessful.
Additionally, the industry has noted the use of chemicals and/or secondary processes to treat the wood chips for greater ease of processing, for example, as described in U.S. Pat. No. 4,767,499 (Simonson et al.); U.S. Pat. No. 2,947,655 (Eberhardt); and a technical article titled “Groundwood Mills use Specialty Chemicals to Solve Pitch Problems” Pulp & Paper, by Rying, S., March 1978, p. 177-179.
The embodiments of the process provided by the present invention address the needs of the papermaking industry due to the enhancement of the refiner production rate and/or the reduction of the specific energy necessary for a freeness target. The embodiments of the present invention provide costs savings with respect to the number of refiners needed in a given process to produce a particular tonnage of pulp per day as well as a potential reduction in the energy consumption for the refining process.
Additionally, the embodiments of the present invention are advantageous because they do not pose a health risk to operators of the refiner because highly alkaline and toxic substances such as sodium aluminate are not used.